1. Field of the Invention
This invention relates to airless paint spraying equipment and more particularly to a safety nozzle assembly for such equipment.
2. Description of the Prior Art
Airless paint spraying has recently become an important segment of the paint spraying equipment market. Such "airless" equipment propels only paint, or other fluid to be sprayed, through a spray nozzle without admixture of air. Because only sprayed fluid, exits the nozzle rather than the more normal combination of air and paint, "airless" systems have numerous advantages.
However, it has been found in certain exceptional instances, that injury can occur from the use of such airless systems. One common feature of airless equipment is the high pressure at which the sprayed fluid stream is forced through the nozzle opening. Pressures on the order of 175-210 kilograms per square centimeter (2500-3000 p.s.i.) have been encountered in connection with small hand-held electric spray guns and normal operating pressures between 112 and 155 kilograms per square centimeter (1600 and 2200 p.s.i.) are common to such units.
At such pressures, the exiting stream of fluid can penetrate the skin of a user. Where the sprayed fluid is toxic, this penetration can have adverse effects upon the user.
During experimentation, we have found that penetration can occur in one of two ways. One form of penetration occurs when the user covers the nozzle, usually with a finger, for purposes of cleaning the nozzle or otherwise. If the spray gun is actuated at such time with the finger in contact with the nozzle opening, penetration of the skin can occur. A second type of penetration occurs when the spray equipment is operating and a stream of fluid is being ejected. At such time, if the user's skin passes through the stream, either by accidentally misdirecting the gun, or otherwise, penetration can also occur. However, we have found, during experimentation, that critical distances are involved and that unless the user's skin is positioned sufficiently close to the nozzle opening, no penetration will occur.
In tests using the shaved skin of a rabbit, it has been determined that paint sprayed from a small "airless" hand-held unit can penetrate the skin spreading out along the underlying fascia but not penetrating the underlying muscle when the nozzle tip was placed directly against the skin and the unit thereafter activated. Such small units are known, in the industry, as cup guns. Examples of such guns are shown in U.S. Pat. Nos. 3,116,879; 3,445,068 and 3,680,789 all issued on applications of Josef Wagner.
Such cup guns include a body member with a depending handle from which a removable paint container is suspended. The body member includes an electric motor having a vibrating member, such as an armature, which drives a paint propelling member, either a piston or a liquid or dry diaphragm, which on one stroke sucks paint from the container into a cylinder and which on the opposite stroke forces the paint from the cylinder through a nozzle attached to the body member. Both the stroke of the oscillating member and the size of the spray nozzle opening are variable providing variance in pressures, delivery rates and spray patterns. However, in the vast majority of instances, the spray nozzles have a final circular opening therein. A typical nozzle is shown in U.S. Pat. No. 3,116,879.
Many of such devices operate by forcing the paint through the nozzle opening at a high velocity such that the paint is immediately atomized downstream of the gun. In order to produce effective atomization, and the desired high velocities, it is necessary to propel the paint or other fluid to be sprayed by the application of a very high pressure. Since the paint exits through a circular nozzle opening on the order of 0.28 millimeters to 1.8 millimeters (0.011 to 0.072 inches) in diameter, the resultant stream, although pulsed due to the reciprocating action of the piston, can act in the manner of a hypodermic and pierce human skin.
However, because of the atomization of the paint, and because the natural fluid flow downstream from the opening is in the shape of a cone, this ability to act as a hypodermic is directly proportional to distance from the nozzle opening to the skin. There is therefore a critical distance area beyond which no skin penetration will occur but within which penetration can, in unusual instances, occur.
Although, in other embodiments, not dealing with airless cup gun spraying equipment, nozzle designs have evolved which include projections extending beyond the nozzle opening, such designs have not been concerned with preventing injection nor have they been dimensioned adequately to provide anti-injection features. Examples of prior art nozzles having projections extending beyond the nozzle opening are U.S. Pat. No. 3,754,710 to Chimura; U.S. Pat. No. 3,836,082 to Krohn; U.S. Pat. Nos. 3,780,953 and 3,844,487 to Malec and other similar devices dealing with paint spray equipment. In addition, air guns have also been provided with projections for purposes entirely different from preventing injection. See for example U.S. Pat. No. 2,597,573 to De Groff and U.S. Pat. No. 3,599,876 to Kyburg.
It would therefore be desirable to provide a safety apparatus which would prevent occurrence of penetration within the critical area.
Additionally, in the design of a protective tip apparatus, it may be advantageous to provide means for preventing both accidental contact between a paint stream exiting the nozzle opening and the skin of a user and contact resulting from misuse of the spraying equipment such as, for example, placing one's finger over the opening and initiating operation of the paint sprayer in a mis-guided attempt to test pressure build-up or to test operation or to clean a fouled tip. The prior art has not attempted to provide solutions to such accidental or intentional contacts.